GRIM II NICMOS3 Detector

Introduction

GRIM II's detector is a Rockwell 256x256 NICMOS3 HgCdTe array sensitive from 1-2.5 microns. The array's properties are summarized below.

                 GRIM II Array Characteristics
     =====================================================
     Item                    Description
     -----------------------------------------------------
     Array size              256 x 256 pixels
     Pixel size              40 microns x 40 microns
     Spectral range          1 - 2.5 microns
     Quantum efficiency(1)   approx. 70%
     Gain(2)                 4.73 +- .2 e- A.D.U.^-1
     Read noise(2)           110 +- 20 e-
     Linear well depth (3)   130,000 e-
     Dark current            < 1 e- sec.^-1
     =====================================================
     Notes: (1) Rockwell measurement
            (2) Quadrant 4
            (3) 28,000 A.D.U. above bias

Linearity

Click to see the Linearity Plot

Read Noise & Gain

The electronic gain and read noise were measured using the photon transfer technique (Janesick, Klaasen, & Elliott 1987). The photon transfer technique uses the data's noise properties to measure the read noise and gain.

Click to see the Photon Transfer Plot

GRIM II uses a correlated double sampling (CDS) readout scheme. Each "exposure" consists of two "reads". The first read occurs at the start of the exposure. The second "read" occurs a the end of the exposure. Moreover, the HgCdTe diodes are accessed twice during each "read". One could therefore define the "read noise" in a number of ways.

The read noise reported here is for a full CDS exposure like an observer would take.

References

Janesick, J.R., Klaasen, K.P., and Elliott, T. 1987, Optical
     Engineering, 26(10), 972